1. Field of Invention
The invention relates to a method for producing a rotationally symmetrical hollow part, particularly a shaft or a transversally spline-rolled rotationally symmetrical hollow part.
2. Description of Related Art
The production of rotationally symmetrical hollow parts from solid material which can also serve, for example, as a preform for further forming, like stepped shafts, especially of a transmission shaft by transversal spline-rolling is increasingly executed. It is executed on plane jaw or round jaw machines. These transversally spline-rolled shafts are hardened by a rolling process performed on its periphery. By the use of solid material, a high weight is obtained, which is undesirable especially in the application of these kinds of shafts in the automotive industry. Transmission shafts are also costly when produced by round kneading machines from hollow shafts and then welded or the shafts are mechanically machined (deep-hole drilled).
Typical devices for the transversally spline-rolling of bars are known from East German Patent DD 99 521. Reference is made to this document to the full extent in order to avoid repetitions. In this patent, a heated bar is progressively machined between rollers wherein mandrels are arranged coaxially the rolling axis of the material and oppositely as a stopper part and as a support part and at least one mandrel being axially movable on the opposite side of the other. The axially arranged mandrels provide only supporting devices and optionally as processing devices for the end sectors or the bar—the production of a bore-hole or a through bore-hole or of a hollow part is not possible.
According to German Patent Application DE 10308849 A1, the forming production of rotationally symmetrical hollow parts in true form and net-shape from semi-finished products of bar-shaped solid materials is performed by pressing the hole using a pressing mandrel and a slide equipped with at least two pressing rolls, wherein the semi-finished product is purposefully heated before the forming process and after that is cooled whereby a desired temperature gradient from the core zone of the semi-finished product to its mantle surface is obtained; the forming zone of the emerging hollow body is cooled in order to increase the strength of the material with sufficient ductility and the hollow body is then exposed to a heat treatment with a controlled temperature profile in order to increase the strength and the toughness of the material—here of iron alloys—and in order to improve the endurance strength. Also costly temperature guidance is necessary for the execution of this process.
According to German Patent Application DE 19905038, a transversal rolling device equipped with a mandrel device is known, although in this document, there are no indications about the process parameters, like temperature or duration or about the material to work with the described mandrel device indicated there for the production of shafts in order to be able to produce a hollow part.